if you don't have network,
on other PC on network, download the current grub-pc package from
http://packages.debian.org/sid/grub-pc (near end of the page) for your
architecture (i.e. now grub-pc_1.98+20100804-4_i386.deb)
copy it on somewhere in above chroot environment, move to that folder
dpkg -i grub-pc_1.98+20100804-4_i386.deb

if you don't have network,
on other PC on network, download the current grub-pc package from
http://packages.debian.org/sid/grub-pc (near end of the page) for your
architecture (i.e. now grub-pc_1.98+20100804-4_i386.deb)
copy it on somewhere in above chroot environment, move to that folder
dpkg -i grub-pc_1.98+20100804-4_i386.deb